When most people hear through the news media of an impending meteor shower, likely their first impression is of a sky filled with shooting stars pouring down through the sky like rain.
Such meteor storms have indeed occurred with the famous November Leonids, such as in 1833 and 1966 when meteor rates of tens of thousands per hour were observed. In more recent years, most notably 1999, 2001 and 2002, lesser Leonid displays of up to a few thousand meteors per hour took place.
Those turn-of-the-century Leonid showers — and their accompanying hype — are still remembered by many. Every year at this time, there is always a ripple of excitement in the knowledge that the peak of the Leonid meteor shower is approaching.
So, I think it is important to stress here at the outset that any suggestion of a spectacular meteor Leonid display this year is, to put it mildly, overly optimistic.
In fact, the 2021 version of the Leonids, scheduled to crest on Wednesday morning (Nov. 17), are likely to be a major disappointment, partly because of the expected lack of any significant activity, but mainly because of the moon, which unfortunately will be less than two days from full, flooding the sky much of the night with its bright light.
So, although the Leonids are one of the most famous of all the annual meteor displays we certainly would not advertise them as a major shower this year, especially to a newcomer to meteor observing, since they likely will be weak and badly affected by the intense moonlight.
The Leonids are so named because the shower's radiant point, from where the meteors seem to fan out, is located within the constellation of Leo, the lion. The meteors are caused by Comet Tempel-Tuttle, which sweeps through the inner solar system about every 33 years. Each time the comet passes closest to the sun it leaves a "river of rubble" in its wake; a dense trail of dusty debris. A meteor storm becomes possible if the Earth were to score a direct hit on a fresh dust trail ejected by the comet over the past couple of centuries.
But the 2021 Leonids are expected to show only low activity this year with at best 10 to maybe 20 meteors per hour. But as we've already noted, the "traditional" peak for the Leonids is scheduled for the predawn hours of Wednesday, Nov. 17 and the bright moon will be shining brightly like a spotlight in the western sky within the constellation of Pisces, the fishes, making observations difficult.
How to observe and what to look for
Watching a meteor shower consists of lying back, looking up at the sky and waiting. In addition to this year's handicap of a bright moon lighting up the sky, keep in mind that any local light pollution or obstructions like tall trees or buildings will further reduce your chances of making a meteor sighting.
Leo does not start coming fully into view until the after-midnight hours, so that would be the best time to concentrate on looking for Leonids. Also, because they are moving along in their orbit around the sun in a direction opposite to that of Earth, they slam into our atmosphere nearly head-on, resulting in the fastest meteor velocities possible: 45 miles (72 kilometers) per second. Such speeds tend to produce bright meteors, which leave long-lasting streaks or vapor trains in their wake.
Still, a mighty Leonid fireball can be quite spectacular and bright enough to attract attention even in the bright moonlight. But such outstandingly bright meteors are likely to be very few and very far between this year.
So, here's the bottom line: If you plan to brave the chill of a mid-November morning, a moonlit sky and the prospects of catching a glimpse of only a few Leonids, you should get an award for perseverance.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.